This could be as simple as person B previously enabled remote WAN management of the router. Person B knows the router's external IP address and password. He can login and reboot it remotely, resulting in "several minute" outage.
Another possibility is person B is aware of a DOS attack which affects this router triggering a reboot.
Fix: update firmware, ...
The problem with SQL injection is not how the data are stored in the database but that
statements in the query language are code and data combined into a string
these statements are often constructed by manually combining strings of code with strings of untrusted data
improper validation of the untrusted data leads to interpretation of these data as code, ...